2001-04-11 04:00:00 PDT Oakland -- At Oakland's King Estates Middle School - where most students are minorities and come from low- or middle-income families - seven of the 27 teachers have full teaching credentials.

In contrast, at Orinda Intermediate School in Contra Costa County, all 46 teachers have been through teacher training and are fully credentialed. The 903-student school is predominantly white, and nearly all the children come from affluent homes.

Study after study indicates that the most important factor for a student's success is a quality teacher in the classroom. But throughout California, nearly 13 percent of the 292,055 classroom teachers are working with emergency credentials that require only a bachelor's degree and a passing score on a test set at about a 10th-grade level.

And in general, it is poor and minority students who get the least qualified teachers.

At Orinda Intermediate, 6 percent of the teachers are in their first year, while at King Estates, 40 percent are new to the profession.

Statewide, schools with the highest poverty and the lowest achievement have,

on average, 22 percent of their teaching staffs working without full credentials. That compares with the highest achieving schools, where only 4 percent of the teachers are underqualified, according to a study by the Center for the Future of Teaching and Learning.

The connection between excellent teaching and student success, cannot be minimized, experts say.

Disadvantaged students who spend four consecutive years with a good teacher can bridge the performance gap separating them from affluent students for whom good teaching is the norm, studies show.

"You can erase the average difference between a kid from a low-income family and an upper-income family," said Eric Hanushek, a senior fellow at Stanford University's Hoover Institution.

But students who have rookie teachers year after year will continue to slip further and further behind.

"Many children are already two to three years behind suburban peers," "If you place them with three consecutive poor teachers, they never recover," said Aida Walqui, director of teacher professional development at WestEd, a San Francisco consulting firm.

Fourth-graders in Dallas who were assigned to three highly effective teachers in a row rose from the 59th percentile in fourth grade to the 76th percentile by the end of sixth grade, according to a paper by Kati Haycock, director of the Education Trust. Students assigned three consecutively ineffective teachers fell from the 60th percentile in fourth grade to the 42nd percentile by the end of sixth grade.

In California, the problem has been exacerbated by class-size reduction.

While many hoped that California's push to cut the teacher-student ratio would improve performance, it has instead been devastating to disadvantaged students, Walqui said. As districts scrambled to fill additional slots, most of the qualified, experienced teachers chose to work in the more affluent, suburban districts. Urban districts and those with many minority students were left with untrained teachers.

Shortages have continued and even grown as many veteran teachers reach retirement age.

"In schools where one needs the most expertise, students have been robbed of their qualified teachers," Walqui said. "Obviously, we would also like to have small classrooms, but if you have to choose, we say go for better teachers who are supported."

Teacher quality accounted for 40 percent of student achievement, while smaller class sizes accounted for only 10 percent, said Walqui, citing the findings of a recent Harvard University study by Ronald Ferguson.

Trained teachers are able to use a variety of strategies that respond to students' needs and learning styles, Linda Darling-Hammond reported in a 1999 Stanford study.

Experts agree that if a teacher is not reaching students, smaller classes won't matter.

"If you have an unqualified teacher and you have 20 students instead of 28, that (smaller class size) doesn't make up for it," said Lionel Meno, dean of the College of Education at San Diego State University. "Where you have a qualified teacher in the classroom, that can have a tremendous effect."